Preparation of secondary amines



Patented May 26, 1936 v t UNITED STATES PATENT OFFICE PREPARATION OFSECONDARY AMIINES Waldo L. Semon, Silver Lake Village, Ohio, as-

signor to The B. F. Goodrich Company, New York, N. Y., a corporation ofNew York No Drawing. Application June 23, 1933, Serial No. 677,274

16 Claims. (Cl. 260-128) This invention relates to the art of organicolecular proportions of aniline and pchemistry and particularly to thepreparation of phenol. The mixture is neutralized with caustic certainsecondary aromatic amines. Toda, and the iron oxide is filtered ifromthe hot The methods which have been employed hereq d- After Cooling, themix We aniline and tofore for the preparation of secondary aromatic p-an 1 1s s lo i tt om t aq us 6 amines, particularly those which are notsym- J' fi I eyie 6. may 8 So ewhat nmetrical around the amino group,have frequentcreased by Washing e irOn de Sludge W 1y involved the useof expensive reagents, not a Small q y of hot Water and e p y t sreadily obtainable in large quantities, and the water, containing aCertain q y of o v d 10 yields obtained have frequently been so low asamines, in the reduction 0f the next batch- 10 to increase the cost ofthe products several fold. The Condensation of the aniline With the p-The chief object of this invention is accordingly almihflphehol is ab ycarried out in the to produce secondary aromatic amines from readp c ofan eSS Of a ne, ence an addiily available materials, by a comparativelysimple tiohal I -E y 0f aniline equivalent from 5 process, and at d ttthree to ve times that already present in the This invention, in brief,consists in preparing mixture is added, et er W t a Small q l jL/ amixture of primary aromatic amines by the reof gnden$atincata15t5t7511011715'hydit? Oric duction of 'a suitable azocompound, and then act iodine, Zine e 10ride,e 0. Thus, 200 poundsheating the mixture to induce a condensation of aniline may be added tothe mixture of aniline 0 reaction with the formation of a secondaryamine. and p'amtnophenol obtained as described above,

I The necessity for separating and purifying the together with 1 poundof concentrated hydro individual amines, which is frequently attendedchloric acid and the mixture heated its boiling by considerabledifficulty and expense, is conteglpemturg in t f with? sequently whollyavoided. The invention will re ux con enser' e eno mac 5 best beunderstood by reference to certainspee h the anmtte Pihydroxy diphenyl25 cific examples, which, however, are to be'regarded f bemg ehmmatedrmerely as illustrative of the invention and not quantlty of dtphenyl tdlamme also as limiting its scope. gorrrrlled 1by the fllgfihgfireaction $1 the hyillroizly Exam le 1.-Para-h drox zo benzen 1p eny ammeW1 6 excess W1 8 pared in the usual way by di a otizing aniiil l e grfdzlimmatgm 233 fi gz g q gfi B0 coupling with phenol. For example, 46.5ounds W pro t can e re a y Varymg e of aniline are mixed with 133 poundsof c ncenume of i and to extent by trated hydrochloric acid and allowedto cool. the quantlttf of exces? atuhne Thus It From 300 to 375 poundsof ice are then added to p'hydmgy dtphgnylamme Is the 'deslred productreduce the temperature to 5C., and 37 pounds of fi 1s l g t fi E i 1" 35powdered sodium nitrite are then added slowl Ion o e eno W1 8 am 15 withrapid agitation. A solution of 47 pounds c r tompleted after 4 9 hoursThe mlgture phenol and 22 pounds of caustic soda in about 12 15 thenfractlonauy qlstmed pteterably m gallons of water is next slowly addedand finally vatittummhe hght fractlons contalmmg the exqess the solutionis carefully neutralized with an alamhne and any unreacted p'a'mmophenolbentg 40 kali care being taken not to render it alkaline returned to thenext batch and the phyamxydl' phenylamine being separated from the lessvolapounds of salt are then dissolved in the mlxile dlphenyl p-phenylenedlamlne. If the latter ture to reduce the solubility of the azo compoundcompound is the desired product, the heating is W ich may t b filteredcontinued for a longer time, say 24 hours, and 45 The hydroxy benzenemay be reducedm the hydroxy diphenylamine obtained in the fracany one ofa number of Ways, for instance, With tional distillation is returned tothe next batch iron and hydrochloric acid, with zinc and acid, along iththe excess aniline. with a sulp ide, catelytieally W hyd ogen In analternative modification of this process,

itself. In one method the p-hydroxy azo benthe p-hydroxy azo benzene,instead of being sep- 50 zene prepa as described above is miXed Witharated from the brine by filtration, is separated about 40 gallons of Wacontaining 4 /2 p u ds by extraction with aniline. The entire excess ofof concentrated hydrochloric acid. The mixture aniline which is laterrequired, 200 lbs. in the is heated and pounds of iron are slowly added.specific example given above, is added to the sus- 55 The reducedproduct contains a mixture of equipension of the p-hydroxy a zo benzeneafter the 55 addition of the salt. The p-hydroxy azo benzene dissolvesin the aniline, forming. a supernatent layer which is separated from theaqueous brine. The p-hydroxy azo benzene dissolved in the ani- 5 linemay be reduced by the use of iron exactly as described above, or in anyother suitable way. The catalytic reduction with hydrogen isparticularly advantageous in this modification, for the excess anilineused as a solvent renders the mixture liquid and easy to handle in theordinary hydrogenation apparatus, and because the loss of some of theamines by solution in the aqueous media employed in other methods ofreduction is avoided. The reduced mixture then contains the properproportions of aniline and p-aminophenol and needs only the addition ofhydrochloric acid or such other condensation catalyst as may beemployed, before being heated as described above to initiate thecondensation reaction.

Example 2.Para-amino azo benzene is prepared in the usual way bydiazotizing a large quantity of aniline with a small quantity of nitrousacid to produce diazo-aminobenzene, and

converting the diazo-aminobenzene to p-amino azo benzene by warming itin the presence of acid. For example, 150 pounds of aniline are mixedwith 20 pounds of concentrated hydrochloric acid, and ice is added untilthe temperature is reduced to 25 C. A solution of 10 pounds of sodiumnitrite in 30 pounds of water is slowly added along with enough more iceto maintain the temperature at 25 C. After 2 hours the water layer isremoved, and 16 pounds of aniline to which has been added 1 pound ofconcentrated The mixture is wiloric acid is added.

warme 'fiadually to 40CT6ver aperiod of several hours, and is maintainedat this temperature over night.

The aniline solution of p-amino azo benzene obtained in the manner justdescribed is then reduced, for example, by adding 4 pounds of water andslowly adding 27 pounds of iron while maintaining the temperature at C.After 6 to 8 hours, when reduction is complete, the liquid isneutralized with alkali and the iron oxide sludge is filtered off. Thereduction changes the p-amino azo benzene to a mixture of aniline and.p-phenylene diamine, hence the filtered liquid at this stage consists ofa solution of p-phenylene diamine in a large excess of aniline.

The condensation of the p-phenylene diamine with the aniline is effectedby adding a condensation catalyst such as from to 1 pound ofconcentrated hydrochloric acid, and heating, for example, in anautoclave to a temperature of 290 C. for 6 hours, the ammonia gasproduced by the reaction being preferably blown oif every half hour orhour through a condenser which recovers aniline vapors. The product isfinally fractionally distilled, preferably in a vacuum, the initialdistillate of aniline being recovered for reuse in the process, and theintermediate distillate consisting largely of unchanged p-phenylenediamine and of p-amino diphenylamine being returned to the autoclavewith the next batch. The desired product, diphenyl p-phenylene diamine,distills at 250-280 C. at a pressure of about 4 mm. of mercury.

If desired, p-amino diphenylamine may be prepared in the same way byheating for a shorter time or at a lower temperature, and separating theproduct by fractional distillation.

Other secondary amines can be made in a similar way by reducingsubstituted azo compounds to produce a mixture of aromatic amines andcondensing the mixture to give rise to a secondary amine. The azocompound may even be symmetrically substituted, in which case the twomolecules of amine produced by the reduction will be identical and thefinal secondary amine will likewise be symmetrically substituted, but inthe process of this invention it will generally be found mostadvantageous to employ unsymmetrical azo compounds which give rise todifferent amines and consequently to products which are unsymmetricalsecondary amines. In some cases, as in the specific examples above, theyield of the desired product may be improved by employing an excess ofone of the amines.

In general any aromatic primary amine such as aniline, toluidine,xylidine, cumidine, amino biphenyl, naphthylamine, phenylene, diamine,benzidine, diamino diphenylmethane, anisidine, phenetidine, etc., may bediazotized and coupled with any phenol or aromatic amine containing areplaceable hydrogen in the ortho or preferably the para position,including phenol, cresol, xylenol, thymol, carvacrol, guaiacol, phenylphenol, naphthol, etc. or aniline, toluidine, xylidine, cumidine, aminobiphenyl, naphthylamine, methyl aniline, ethyl aniline, dimethylaniline, benzyl aniline, diphenylamine, anisidine, phenetidine, etc.,and then reduced; or a diazo compound may be prepared and then modifiedin some way before being reduced. For instance, aniline may bediazotized and coupled with phenol to give p-hydroxy azo benzene, whichis then methylated to p-methoxy azo benzene, reduced to a mixture ofaniline and p-anisidine, and finally condensed to give p-methoxydiphenylamine. Other modifications will be obvious to any organicchemist.

While I have herein disclosed certain preferred manners of performing myinvention, I do not thereby desire or intend to limit myself solelythereto, for, as hitherto stated, the precise proportions of thematerials utilized may be varied and. other materials having equivalentchemical properties may be employed if desired without departing fromthe spirit and. scope of the invention as defined in the appendedclaims.

I claim:

1. The method which comprises reducing an azo compound to form a mixtureof primary aromatic amines, and heating the mixture of amines to causethem to condense to a secondary aromatic amine.

2. The method which comprises reducing an unsymmetrically substitutedazo compound to form a mixture of two different primary aromatic amines,and heating the mixture of amines to cause them to condense to asecondary aromatic amine.

3. The method which comprises reducing a hydroxy substituted azocompound to form a mixture of an aminophenol with another primaryaromatic amino compound, and heating the mixture to cause itscondensation to a secondary aromatic amine.

4. The method which comprises diazotizing a primary aromatic amine,coupling with a phenol, reducing the azo compound so produced to form amixture of anaminophenol with another primary aromatic amine, andheating the mixture to cause its condensation to a secondary aromaticamine.

5. The method which comprises diazotizing a mono-aryl amine, couplingwith phenol, reducing the azo compound so produced to form a mixture ofp-aminophenol and. the original monoaryl amine, and heating the mixtureto cause its condensation to a secondary aromatic amine.

6. The method which comprises diazotizing aniline, coupling with phenol,reducing the p-hydroxy azo benzene produced to form a mixture ofp-aminophenol and aniline, and heating the mixture to cause itscondensation to a secondary aromatic amine.

7. The method which comprises reducing an unsymmetrically substitutedazo compound to form a mixture of two different primary aromatic amines,adding in excess of one of the amines to the mixture, and heating themixture to cause its condensation to a secondary aromatic amine.

8. The method which comprises reducing a hydroxy substituted azocompound to form a mixture of an aminophenol and another primaryaromatic amine, adding an excess of the latter amine to the mixture, andheating the mixture to cause its condensation to a secondary aromaticamine.

9. The method which comprises reducing p-hydroxy azo benzene to form amixture of p-aminophenol and aniline, adding an excess of aniline to themixture, and heating the mixture to cause its condensation to asecondary aromatic amine.

10. The method which comprises reducing phydroxy azo benzene to form amixture of paminophenol and aniline, adding an excess of aniline to themixture, and heating the mixture for a limited time to cause itscondensation to p-hydroxy diphenylamine.

11. The method which comprises reducing phydroxy azo benzene to form amixture of paminophenol and aniline, adding an excess of aniline tothemixture, and heating the mixture until the major part of thep-aminophenol has condensed with the aniline to give diphenyl pphenylenediamine.

12. The method which comprises diazotizing aniline, coupling withphenol, extracting the phydroxy azo benzene with aniline, reducing thesolution of the p-hydroxy azo benzene in aniline to form a mixture ofp-amino-phenol with an ex cess of aniline, and heating the mixture for alimited time to cause its condensation to p-hydroxy diphenylamine.

13. The method which comprises diazotizing aniline, coupling withphenol, extracting the phydroxy azo benzene with aniline, reducing thesolution of the p-hydroxy azo benzene in aniline to form a mixture ofp-aminophenol with an excess of aniline, and heating the mixture untilthe major part of the p-aminophenol has condensed with the aniline togive diphenyl p-phenylene diamine.

14. The method which comprises diazotizing a primary aromatic amine,coupling with an arcmatic amine, reducing the azo compound so producedto forma mixture of primary aromatic amines, and heating the mixture tocause its condensation to a secondary aromatic amine.

15. The method which comprises reducing an amino substituted azocompound to form a mixture of an aromatic diamine containing at leastone primary amino group with another primary aromatic amine, and heatingthe mixture to cause its condensation to a secondary aromatic U WALDO L.SEMON.

